This invention relates to bonding valve stems to molded rubber articles such as inflatable products, toys, and in particular envelopes employed in certain types of tire retreading processes.
Numerous procedures have been suggested for attaching valve stems to rubber articles such as inner tubes, bladders, and the like. Sometimes, however, because of imperfect bonding a leakage between the valve stem and its seal with the rubber article destroys the value of the finished article. Typical of the prior art devices or procedures are shown in the U.S. Pat. Nos. to Mincher 1,671,306, Broecker 2,106,673, and Becker 2,143,837. These prior art patents disclose various techniques for either attaching a rubber disc to the valve stem and then attaching the resulting composite structure to the rubber article or attempting to vulcanize a valve stem and disc together with the rubber article in a single operation wherein the opening in the valve stem is aligned with an opening in the rubber article. These prior art teachings require precision alignment of the various elements being assembled prior to curing and some errors result in less secure bonding so that leaks occur from time to time in the finished product. Also, the passageway through the valve stem may become partially blocked during the curing process. Of more general interest are the U.S. Pat. Nos. to Bourdon 2,495,955 and Pratt 3,247,882. In all these prior art teachings the stem is assembled with the article by lining up the passage through the stem with an aperture in the article.
The present invention is an improvement over these teachings in providing a method for simultaneously vulcanizing the stem and the rubber article together in the presence of an uncured valve base material. A mold assembly is provided including a main mold adapted to receive a valve stem mold and the article, the latter being generally in the form of a sheet. In such an assembly, the valve stem with a removable plug is inserted into an uncured rubber ring and then fitted into the valve stem mold which has a suitable molding chamber for receiving the stem and the uncured rubber ring in a manner such that the plugged end of the valve stem will be nearly flush with the mold cover. This assembly of the valve stem and ring in the mold, including the plug is then completely covered with a portion of the uncured rubber article and the entire assembly is pressed under curing conditions in the main mold so that the stem is bonded to the article by simultaneous curing of the ring and the article. After this curing process has taken place, the plug which was inserted in the end of the valve opening is pushed clear of the passageway through the valve stem, and as it is pushed clear it shears away a small portion or circular plug of the cured article material. The separated plug of cured material and the plug may be disposed of so that the passageway through the valve stem is fully opened to the opposite side of the article.
It is therefore an object of this invention to provide an improved curing method for attaching valve stems to rubber articles and more particularly for attaching metal valve stems to a rubber sheet during vulcanization of the rubber sheet.
It is another object of this invention to provide an improved assembly and curing procedure for assembling a metal valve stem with a rubber article to produce a leak-proof seal between the stem and article while insuring a clear valve stem passage in the final product.